1. Field of the Invention
This invention relates to a semiconductor laser device and a heat sink used therein.
2. Description of Related Art
A semiconductor laser device in a range from several watts to a few tens watts has often used a water-cooled system therein in order to implement high-power and high-reliability. Micro channels are well known as heat sink structures because they increase heat-removing efficiency.
Fine interior channel structures such as micro channels are typically formed by etching a pattern onto thin metal plates and laminating the plates together. Diffusion bonding or brazing is generally used to bond the thin metal plates together. As Copper plates are commonly used as the thin metal plates because they have excellent thermal conductivity and easy machinability.
Copper has a thermal expansion coefficient of, 17*10−6/k while a substrate of gallium arsenide, which is generally used in a high-power semiconductor laser device, has a thermal expansion coefficient of, 5.9*10−6/k. This large difference between the thermal expansion coefficients causes a stress to occur when a semiconductor laser chip is fixed to a heat sink with solder and then they are cooled to the normal temperature.
It is known that, turning on electricity through the semiconductor laser chip with any stress occurring in the chip, accelerates the number of crystalline defects, thereby reducing the reliability of the laser.
In order to solve the problem, a soft solder, for example, indium solder is used or a sub mount made of copper tungsten or the like, which has a thermal expansion coefficient close to that of the semiconductor laser chip, is inserted into a position between the heat sink and the laser chip (see Japanese Patent Application Publication No. 2004-186527).